The present embodiments relate to a transmitter for pilot tone navigation in a magnetic resonance tomography system and to a method for identifying patient movements.
Magnetic resonance tomography systems are imaging apparatuses that, in order to map an examination object, align the nuclear spins of the examination object with a strong outer magnetic field and by a magnetic alternating field excite the same for precession about this alignment. The precession or return of the spins from this excited state into a state with less energy generates, as a response, a magnetic alternating field that is received via antennae.
With the aid of magnetic gradient fields, a spatial encoding is impressed onto the signals, which then permits an assignment of the received signal to a volume element. The received signal is then evaluated, and a three-dimensional imaging representation of the examination object is provided.
Depending on the pulse sequence used, also referred to as sequence, the image capture in a magnetic resonance tomography system requires a number of milliseconds up to seconds. A longer capture time usually results in minimal noise artifacts. The image capture may be started in each case at the start of a phase, in which the body remains relatively still, in order to avoid motion artifacts due to a movement during the image capture. Unavoidable movements are, for example, breathing and heartbeat. However, a phase of relative rest (e.g., after breathing out or a contraction of the cardiac muscle) also follows a phase with movements. An image capture in this phase is to expect a relatively long time frame with few movements so that the best measurement results are to be expected.
It is known to capture the movements using mechanical sensors or using electrodes, for example, that measure the excitation potential of the muscles.
The German patent application with the application reference number 102015203385 describes a basic method of capturing the movements using a high-frequency signal. The signal is permanently captured in a patient recording of a magnetic resonance tomography system, and signal changes due to movements (e.g., due to changing interferences or damping) are evaluated. A movement of the patient, caused by breathing or heartbeat, may then be identified from certain patterns of this signal.
The surrounding area of a magnetic resonance tomography system with respect to the irradiation stability is challenging, at the same time the method used places particular demands on the signal source, in order to enable movements to be easily identified.